The major emphasis of our continued studies on the effects of cholera enterotoxin on cultured adrenal tumor cells will be on the nature of the interaction between the toxin and the adrenal cell membrane. This interaction will be analyzed primarily through use of radiolabelled toxin, determining receptor numbers, specificity, and the effects of various degradative enzymes (e.g. phospholipases, proteases, glycosidases) on the binding process. The role of GM1 ganglioside, the apparent receptor in most cell types studied but perhaps not so in these adrenal cells, will be assessed by quantitative metabolic studies, the appearance of radiolabelled toxin into GM1-containing fractions, and the use of cell mutants defective in GM1 synthesis. Cell mutants will also be utilized to delineate the specificity of binding of toxin and of its subunits, and the membrane enzyme systems required to mediate the toxin's cellular effects. The effects of interferon and of virus infection on alteration of the toxin's binding characteristics and cellular activities will also be studied. Further studies of any ultrastructural and of the morphological changes accompanying the toxin's interactions with adrenal cells will be conducted as well, with special attention devoted to the obligate role of adenylate cyclase, cyclic AMP, and/or protein kinase in mediating these effects.